In a typical lumber mill or planer mill, each board is moved along sideways, that is, oriented transversely on a lugged transfer prior to trimming. Typically, the lugs on the lugged transfer are evenly spaced at precise intervals. The boards are passed through an electronic scanner which determines the shape of each board and sends the shape information to an optimizer. The optimizer in turn sends the information to a controller. The controller activates saws above a trimmer saw deck to trim the board, in an attempt to maximize board utilization. Typically, however, saws are spaced about two feet apart, so that depending upon the physical end defects of a board, up to almost two feet on each end of the board can be trimmed and thus wasted, which can result in a considerable wastage of useful wood.
In order to minimize such wastage, in the prior art, board positioners have been developed which utilize a plurality of parallel rollers that are driven in a direction at right angles to the transfer deck, thus moving the ends of the boards up to a positioning fence. When on the rollers, the boards are continually thrust laterally across the transfer deck, until the board is raised above the rollers thus disengaging the board from the rollers at a predetermined time. Such prior art devices have the disadvantage that wet or icy boards will often slip on the rollers while being moved. Such slippage is exacerbated by the rapid rotational acceleration of the rollers as the rollers are accelerated to thrust, lengthwise, the boards laterally across the transfer deck. In addition, such devices suffer from the fact that tapered ends of the boards abutting the positioning fence can be so structurally weak as to collapse or break when contacting the fence. Because the board was scanned and optimized based on the inclusion of the tapered ends, if one end is broken off, the optimized lengthwise movement of the board can be overshot as the broken board is ended against the positioning fence, resulting in a board that is trimmed non-optimally.
Thus, it is the object of the present invention to provide a board positioning device which can accurately position selected boards lengthwise, and process the boards through the trimmer at a higher rate of speed than prior art devices and without substantial slippage, or collapse of the board's weak ends, to thus provide an improvement in maintaining a consistently accurate and optimally trimmed board.
Further, if the board is translated laterally by the rollers more than a small distance before the board contacts the positioning fence, the lateral velocity and acceleration of the board will often result in the board bouncing off the positioning fence. This also causes loss of accuracy in optimizing trimming of the board because the optimizer and controller regulating the lateral optimized positioning of the board relative to the saws uses positioning information based on the assumption that the board is ended closely against the positioning fence.
Thus, it is the object of the present invention to provide a board positioning device which can accurately position selected boards lengthwise, that is, transversely across the transfer deck and process the boards through the trimmer at a higher rate of speed than prior art devices and without substantial board slippage or bounce, or collapse of the board's weak ends, to thus provide an improvement in maintaining a consistently accurate and optimally trimmed board.